The emergence of Petascale systems has raised new challenges to performance analysis tools. Understanding every single detail of an execution is important to bridge the gap between the theoretical peak and the actual performance achieved. Tracing tools are the best option when it comes to providing detailed information about the application behavior, but not without liabilities. The amount of information that a single execution can generate grows so fast that it easily becomes unmanageable. An effective analysis in such scenarios necessitates the intelligent selection of information. In this paper we present an on-line performance tool based on spectral analysis of signals that automatically identifies the different computing phases of the application as it runs, selects a few representative periods and decides the granularity of the information gathered for these regions. As a result, the execution is completely characterized at different levels of detail, reducing the amount of data collected while maximizing the amount of useful information presented for the analysis.